1. Field of the Invention
The present invention relates to an electronic control unit for car having the so-called self-shut OFF function for, when turning off an ignition switch (IGN SW) to supply or interrupt a constant voltage to a circuit in the electron control unit for car, detecting it by a central processing unit (CPU) and interrupting the supply of the constant voltage (VCC) to the internal circuit after a predetermined time using a control signal from the central processing unit (CPU).
2. Prior Art
Patent Document 1: Japanese Application Patent Laid-open Publication No. 2000-172384
Patent Document 2: Japanese Application Patent Laid-open Publication No. Hei 11-132086
Conventionally, a system is used for turning on an ignition switch (IGN SW), transforming a supply voltage (VIGN) from a battery to a constant voltage (VCC) by a power source IC via the ignition switch (IGN SW), and then supplying the constant voltage (VCC) to the internal circuit. Further, the system, using a function (a self-shut OFF function) for inversely turning off the ignition switch (IGN SW), detecting interruption of the supply of the supply voltage (VIGN) by the central processing unit (CPU), and interrupting the supply of the constant voltage (VCC) to the internal circuit after a predetermined time, outputs a control signal to the power source IC from the central processing unit (CPU), then puts the power source IC into the non-operation state, and interrupts the constant voltage (VCC) to be supplied to the internal circuit. By these operations, the constant voltage (VCC) is supplied to or interrupted from the electronic control unit for car.
The problems of the prior art will be explained by referring to FIGS. 14 and 15. FIG. 14 is a circuit block diagram thereof. When an ignition switch SW3 is turned on, a VIGN voltage 3a immediately transfers a signal 7a from the ignition switch SW3 to a power source IC 6 via a diode 7. By doing this, the power source IC 6 is switched to the operation state and starts supply of an inner constant voltage (VCC) 6a into an electronic control unit for car 1. Thereafter, when the ignition switch SW3 is turned off, the signal 7a for controlling the power source IC 6 is controlled by a control signal 9a from a CPU 9 instead of the VIGN voltage 3a due to the OR circuit constitution of the diode.
FIG. 15 is a timing diagram of the aforementioned block diagram, showing that when the VIGN voltage 3a is changed from an LO signal to an HI signal, the signal 7a controlling the power source IC 6 is also changed immediately to an HI signal. At this time, the power source IC 6 is switched to the operation state and starts supply of the inner constant voltage (VCC) 6a into the electronic control unit for car 1. Further, when the VIGN voltage 3a is changed from the HI signal to the HI LO signal, the CPU 9 detects it and the control signal 9a from the CPU 9 puts the power source IC 6 into the non-operation state after a lapse of a predetermined time of Delay 1 to interrupt the supply of the inner constant voltage (VCC) 6a. However, when the line of the control signal 9a from the CPU 9 is fixed to high due to an unexpected situation, even if the VIGN voltage 3a is changed from the HI signal to the LO signal, the signal 7a controlling the power source IC 6 is fixed to high, thereby cannot put the power source IC 6 into the standby state. Therefore, by a battery voltage 4a, the power source IC 6 cannot be put into the non-operation state. As a result, the inner constant voltage (VCC) 6a is always supplied into the electronic control unit for car 1. It is indicated by a dotted line (right half) shown in FIG. 15.
The Patent Document 1 mentioned above discloses an art of surely stopping a car computer according to the OFF operation of an accessory power source (ACC power source). The art has two timers and has a means for stopping the computer when the first waiting time elapses and the shut-down process is not performed. And, the art has a second timer, when the OFF operation is performed, for starting measurement of the second waiting time longer than the first waiting time. And, the art, when the second waiting time elapses, interrupts the power source of the computer. Therefore, the power source is interrupted only by the second timer.
Further, the Patent Document 2 discloses that when a plurality of controllers are connected with communication lines, on the basis of the key switch state, the controllers control power supply to the engine control unit and engine starting means.